Security integrated circuits, commonly known as “security chips”, are of use to those wanting to protect information, data transmissions or value (typically monetary). These security chips protect data by storing it in secure memory or transmit data securely through the use of cryptography implemented on chip. There are many reasons for using these products including secure banking cards, secure access systems and secure personal identity systems. It is known in the art to protect these chips from invasive attacks whereby criminals and other agents attack the card to try to obtain, change or use secret information on the card.
One type of attack involves trying to place contacts onto internal chip nodes in order to read internal data traffic. This may be achieved by probing, using fine needles to break through the surface passivation to reach the fine metal tracks. Alternatively focused ion beam (FIB) may be used to deposit pads of metal onto the tracks for subsequent probing or bonding by wires. However it is achieved, measuring the signals on internal chip nodes represents an attack, and if successful this attack may render the chip and entire system on which it is based, insecure.
Shields to protect a chip from the above attacks exist at present; they are typically divided into two categories, active and passive. Passive shields are simple metal layers over all or part of the circuit and are designed to prevent viewing and probing. Passive shields may be removed by chemical, plasma or other techniques without changing the operation of the circuit. In other words, a passive shield works to deter attackers by making viewing more difficult initially, but will not actively defend itself against removal.
Active shields may look similar or may look more like a network of lines covering all or part of a circuit. If a line or part of the shield is removed, severed or short-circuited to another line, the breach is detected and the chip halts some or all functions.
Active shields may still be breached using, for example, the following technique. An active shield line is identified as above the circuit element to be attacked. The shield line is bypassed using the ability of the FIB system previously mentioned. The bypass is in the form of a diversion track added in parallel to the original shield track. The original shield track may now be removed leaving the new bypass to fool the detection circuit. No circuit break is detected.
The following references are believed to represent the state of the art:
U.S. Pat. No. 4,214,918 to Gat et al;
U.S. Pat. No. 4,583,011 to Pechar;
U.S. Pat. No. 4,766,516 to Ozdemir et al;
U.S. Pat. No. 4,920,402 to Nakaya et al;
U.S. Pat. No. 5,336,624 to Walden;
U.S. Pat. No. 5,468,990 to Daum;
U.S. Pat. No. 5,783,846 to Baukus et al;
U.S. Pat. No. 5,821,582 to Daum;
U.S. Pat. No. 5,824,571 to Rollender et al;
U.S. Pat. No. 5,866,933 to Baukus et al;
U.S. Pat. No. 5,930,663 to Baukus et al;
U.S. Pat. No. 5,973,375 to Baukus et al;
U.S. Pat. No. 6,064,110 to Baukus et al;
U.S. Pat. No. 6,117,762 to Baukus et al;
U.S. Pat. No. 6,294,816 to Baukus et al;
U.S. Pat. No. 6,360,321 to Gressel et al;
U.S. Pat. No. 6,613,661 to Baukus et al;
U.S. Pat. No. 6,720,656 to Matsumoto;
US Published Patent Application 2001/0033012 of Koemmerling et al;
US Published Patent Application 2002/0173131 of Clark JR et al;
PCT Published Patent Application WO 97/29567 of Fortress U & T Ltd.;
PCT Published Patent Application WO 01/50530 of Koemmerling et al;
PCT Published Patent Application WO 01/54194 of NDS Limited;
EP Published Patent Application No. EP 0 585 601 of Hughes Electronics Corporation;
EP Published Patent Application No. EP 0 940 851 of Hughes Electronics Corporation; and
An article entitled “Infineon Introduces Chip Card Controllers for Improved Security of Electronic Identity Cards and Passports”, available on the World Wide Web at www.infineon.com/cgi/ecrm.dll/jsp/showfrontend.do?lang=EN&BV_SessionID=@@@@0590998578.1109855404@@@@&BV_EngineID=ccchadddmlfiddkcflg cegndfifdfoh.0&content_=NEWS&content_oid=107623&news_nav_oid=9979.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.